He was a grandson of Zhao Dun 趙盾 (Zhao Xuanzi 趙宣子) and a son of Zhao Shuo 趙朔 (Zhao Zhuangzi 趙莊子) and served Duke Ping 晉平公 (r. 558-532) as a high minister.

He was born in a time when the duke of Jin wanted to extirpate the house of Zhao. As the sole surviving member of the house, Zhao Wu, just born after his father had been killed, was secretly raised by Zhuang Ji 莊姬, a daughter of Duke Cheng 晉成公 (r. 607-600), in the ducal palace. In 583, Han Jue 韓厥 (Han Xianzi 韓獻子) recommended to Duke Ping making Zhao Wu the heir of the house of Zhao. He was therefore appointed minister commander (qing 卿) and took over command of the new army (xinjun 新軍) and the superior army (shangjun 上軍).

In 548, he was appointed counsellor-in-chief and factual regent of Jin as successor of Shi Gai 士匄 (Fan Xuanzi 范宣子). Zhao Dun valued the time-tested rituals and courtly etiquette more than the younger method of the feudal lords to present each other with tributes and donations. He was therefore highly esteemed as a nobleman acting according to the ancient customs of the Western Zhou period 西周 (11th cent.-770 BCE).

In 546, he met with Qu Jian 屈建, chief minister of Chu 楚, to conclude an alliance. Five years later he organized a meeting of the states of Chu, Qi 齊, Song 宋, Wei 衛, Chen 陳, Cai 蔡, Zheng 鄭, Xu 許 and Cao 曹 at Guo 虢 (near modern Zhengzhou 鄭州, Henan).